不会做的数学题

D.T.=安仔

我有几个engineering maths的数学题不会做，请各位大家可以赐教一下吗？

2. solve the following equations for angle between 0degree and 360 degree.
   iii) 3cos2θ + sinθ – 1 = 0

4. Differentiate the following with respect to x.

ii) y = ln(4x2)

7. By using Quotient Rule, show that d   (tan 2x) = 2 sec2x .
                                                        dx

8. Prove that cot A + tan A = 2 cosec2 A

各位大大，帮帮忙。。急着下的。。在下先致上万二分感激

jinqwem

2.cos(2x)=1-2(sin(x))^2
过后是QUADRATIC EQUATION, ...
4. dy/dx = 1/(4x^2) * ( d(4x^2)/dx)
         = 8x/4x^2
         = 2/x...
7. tan2x= sin2x/cos2x...
so using quotiont... u = sin2x, v=cos2x.
d(u/v)dx = ( v*du/dx- u*dv/dx)/v^2
8. cotA= cosA/sinA, tanA=sinA/cosA
cotA + tanA =cosA/sinA + sinA/cosA
            = (cosA)^2/sinAcosA + (sinA)^2/sinAcosA
            = (cos^2(A)+ sin^2(A))/sinAcosA
            = 1/sinAcosA
            = 2/2sinAcosA
            = 2/sin2A
            = 2 cosec2A...
注意,cos^2(A)+ sin^2(A)=1, SIN2A=2SINACOSA...

D.T.=安仔

thx4ur help

problem solved